Question

Which two of the following five physical parameters have the same dimensions?
(i) Energy density
(ii) Refractive index
(iii) Dielectric constant
(iv) Young’s modulus
(v) Magnetic field

A. (ii) and (iv)
B. (iii) and (v)
C. (i) and (iv)  
D. (i) and (v)
Answer :   (i) and (iv)
Solution :
$$\eqalign{ & {\text{Energy density = }}\frac{{{\text{Energy}}}}{{{\text{Volume}}}} \Rightarrow u = \frac{E}{V} \cr & {\text{Dimensions of }}u = \frac{{{\text{Dimensions of E}}}}{{{\text{Dimensions of }}V}} \cr & = \frac{{\left[ {M{L^2}{T^{ - 2}}} \right]}}{{\left[ {{L^3}} \right]}} \cr & = \left[ {M{L^{ - 1}}{T^{ - 2}}} \right] \cr} $$
Refractive index is a dimensionless quantity. Dielectric constant is a dimensionless quantity.
$$\eqalign{ & {\text{Young's modulus}}\,{\text{ = }}\frac{{{\text{Longitudinal stress}}}}{{{\text{Longitudinal strain}}}} = \frac{{\frac{F}{A}}}{{\frac{{\Delta l}}{l}}} \cr & = \left[ {M{L^{ - 1}}{T^{ - 2}}} \right] \cr & {\text{Magnetic field = }}\frac{{{\text{Force}}}}{{{\text{Charge}} \times {\text{Velocity}}}} = \frac{F}{{qv}} \cr & = \frac{{\left[ {ML{T^{ - 2}}} \right]}}{{\left[ {AT} \right]\left[ {L{T^{ - 1}}} \right]}} \cr & = \left[ {M{T^{ - 2}}{A^{ - 1}}} \right] \cr} $$

Releted MCQ Question on
Basic Physics >> Unit and Measurement

Releted Question 1

The dimension of $$\left( {\frac{1}{2}} \right){\varepsilon _0}{E^2}$$  ($${\varepsilon _0}$$ : permittivity of free space, $$E$$ electric field)

A. $$ML{T^{ - 1}}$$
B. $$M{L^2}{T^{ - 2}}$$
C. $$M{L^{ - 1}}{T^{ - 2}}$$
D. $$M{L^2}{T^{ - 1}}$$
Releted Question 2

A quantity $$X$$ is given by $${\varepsilon _0}L\frac{{\Delta V}}{{\Delta t}}$$   where $${ \in _0}$$ is the permittivity of the free space, $$L$$ is a length, $$\Delta V$$ is a potential difference and $$\Delta t$$ is a time interval. The dimensional formula for $$X$$ is the same as that of-

A. resistance
B. charge
C. voltage
D. current
Releted Question 3

A cube has a side of length $$1.2 \times {10^{ - 2}}m$$  . Calculate its volume.

A. $$1.7 \times {10^{ - 6}}{m^3}$$
B. $$1.73 \times {10^{ - 6}}{m^3}$$
C. $$1.70 \times {10^{ - 6}}{m^3}$$
D. $$1.732 \times {10^{ - 6}}{m^3}$$
Releted Question 4

Pressure depends on distance as, $$P = \frac{\alpha }{\beta }exp\left( { - \frac{{\alpha z}}{{k\theta }}} \right),$$     where $$\alpha ,$$ $$\beta $$ are constants, $$z$$ is distance, $$k$$ is Boltzman’s constant and $$\theta $$ is temperature. The dimension of $$\beta $$ are-

A. $${M^0}{L^0}{T^0}$$
B. $${M^{ - 1}}{L^{ - 1}}{T^{ - 1}}$$
C. $${M^0}{L^2}{T^0}$$
D. $${M^{ - 1}}{L^1}{T^2}$$

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